我已尽力找到一个简单,相关且最新的示例,该示例适用于最新版本的Firefox,但我确实很努力。
标题确实说明了一切。我希望用户能够从诸如Windows Paint的编辑器中复制图像的一部分,或使用“打印屏幕”按钮,然后将其粘贴到canvas元素中。如果画布调整大小以完全适合粘贴的图像(字面上),则奖励积分。
如果合理,希望避免使用基于Flash或Java的解决方案。
我对Javascript的看法还不错,但是对HTML5的最新功能相对缺乏经验,并且对Canvas元素来说是全新的。请帮忙!
2.0版:较小,更简洁的代码可在Chrome,Firefox,Edge,Opera上使用。不再有骇客。但是,如果需要支持IE和Safari,请检查v1版本。
http://jsfiddle.net/viliusl/xq2aLj4b/5/
Chrome 版本1.0的实现非常简单。Firefox(和IE)具有以下限制:用户必须发出命令才能执行粘贴操作(例如键盘事件),并且必须将可编辑的输入聚焦,因此,我们在这里做一些技巧-在ctrl下,将焦点集中在输入字段上,在释放非焦点上。
浏览器支持(图像数据):
var CLIPBOARD = new CLIPBOARD_CLASS("my_canvas", true);
/**
* image pasting into canvas
*
* @param {string} canvas_id - canvas id
* @param {boolean} autoresize - if canvas will be resized
*/
function CLIPBOARD_CLASS(canvas_id, autoresize) {
var _self = this;
var canvas = document.getElementById(canvas_id);
var ctx = document.getElementById(canvas_id).getContext("2d");
var ctrl_pressed = false;
var command_pressed = false;
var paste_event_support;
var pasteCatcher;
//handlers
document.addEventListener('keydown', function (e) {
_self.on_keyboard_action(e);
}, false); //firefox fix
document.addEventListener('keyup', function (e) {
_self.on_keyboardup_action(e);
}, false); //firefox fix
document.addEventListener('paste', function (e) {
_self.paste_auto(e);
}, false); //official paste handler
//constructor - we ignore security checks here
this.init = function () {
pasteCatcher = document.createElement("div");
pasteCatcher.setAttribute("id", "paste_ff");
pasteCatcher.setAttribute("contenteditable", "");
pasteCatcher.style.cssText = 'opacity:0;position:fixed;top:0px;left:0px;width:10px;margin-left:-20px;';
document.body.appendChild(pasteCatcher);
// create an observer instance
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(mutation) {
if (paste_event_support === true || ctrl_pressed == false || mutation.type != 'childList'){
//we already got data in paste_auto()
return true;
}
//if paste handle failed - capture pasted object manually
if(mutation.addedNodes.length == 1) {
if (mutation.addedNodes[0].src != undefined) {
//image
_self.paste_createImage(mutation.addedNodes[0].src);
}
//register cleanup after some time.
setTimeout(function () {
pasteCatcher.innerHTML = '';
}, 20);
}
});
});
var target = document.getElementById('paste_ff');
var config = { attributes: true, childList: true, characterData: true };
observer.observe(target, config);
}();
//default paste action
this.paste_auto = function (e) {
paste_event_support = false;
if(pasteCatcher != undefined){
pasteCatcher.innerHTML = '';
}
if (e.clipboardData) {
var items = e.clipboardData.items;
if (items) {
paste_event_support = true;
//access data directly
for (var i = 0; i < items.length; i++) {
if (items[i].type.indexOf("image") !== -1) {
//image
var blob = items[i].getAsFile();
var URLObj = window.URL || window.webkitURL;
var source = URLObj.createObjectURL(blob);
this.paste_createImage(source);
}
}
e.preventDefault();
}
else {
//wait for DOMSubtreeModified event
//https://bugzilla.mozilla.org/show_bug.cgi?id=891247
}
}
};
//on keyboard press
this.on_keyboard_action = function (event) {
k = event.keyCode;
//ctrl
if (k == 17 || event.metaKey || event.ctrlKey) {
if (ctrl_pressed == false)
ctrl_pressed = true;
}
//v
if (k == 86) {
if (document.activeElement != undefined && document.activeElement.type == 'text') {
//let user paste into some input
return false;
}
if (ctrl_pressed == true && pasteCatcher != undefined){
pasteCatcher.focus();
}
}
};
//on kaybord release
this.on_keyboardup_action = function (event) {
//ctrl
if (event.ctrlKey == false && ctrl_pressed == true) {
ctrl_pressed = false;
}
//command
else if(event.metaKey == false && command_pressed == true){
command_pressed = false;
ctrl_pressed = false;
}
};
//draw pasted image to canvas
this.paste_createImage = function (source) {
var pastedImage = new Image();
pastedImage.onload = function () {
if(autoresize == true){
//resize
canvas.width = pastedImage.width;
canvas.height = pastedImage.height;
}
else{
//clear canvas
ctx.clearRect(0, 0, canvas.width, canvas.height);
}
ctx.drawImage(pastedImage, 0, 0);
};
pastedImage.src = source;
};
}
1. Copy image data into clipboard or press Print Screen <br>
2. Press Ctrl+V (page/iframe must be focused):
<br /><br />
<canvas style="border:1px solid grey;" id="my_canvas" width="300" height="300"></canvas>
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